(1) Field of the Invention
The present invention relates to a light-impermeable, high purity silicon carbide material to be favorably used as a light shielding member for a semiconductor-treating apparatus.
(2) Related Art Statement
JP-A 10-12,563 discloses that a high-purity silicon carbide-based plate formed by a chemical vapor deposition in a thickness of 0.1 to 1 mm which has the maximum infrared ray transmittance of not more than 5% in the infrared zone is used as a member for thermally treating a semiconductor, and that this member is made of CVD-.beta.-SiC columnar crystals having lengths of 0.1 to 1 mm and CVD-.alpha.-SiC particles having diameters of 0.5 to 5 .mu.m and existing among the columnar crystals. This further discloses that a film of silicon carbide is produced by the chemical vapor deposition, while a raw gas is being fed onto a substrate in a reaction tube and that at that time the high purity CVD silicon carbide film is formed on the substrate at a treating temperature of 100 to 1150.degree. C. while intermittently feeding the raw gas at an time interval of not more than 60 seconds and a ratio between the maximum gas feed rate and the minimum gas feed rate is set at not more than 5, and then the substrate is separated from the film. The member for thermally heating the semiconductor as disclosed in JP-A 10-12,563 has the maximum infrared transmittance of not more than 5% at the thickness of 0.1 to 1 mm, and it is around 1% in Examples.
However, the following problem occurred during the inventors' measurement of the temperatures in the semiconductor-producing apparatuses by using the infrared radiation thermometer. This problem will be explained with reference to a schematic view of FIG. 1.
A susceptor 4 for receiving a peripheral portion of the semi-conductor is supported on an end of a cylinder 5 made of silicon, and a peripheral portion 7a of a seminconductor wafer 7 is supported on the susceptor 4. A heat source (infrared lamp) 1 for heating the semiconductor wafer through a quartz window 2 is arranged at one face side 7a of the semiconductor wafer 7. The other face side 7c of the semiconductor wafer 7 is exposed to a rear face side through a center opening 4a of the susceptor 4. The infrared radiation thermometer 6 is arranged on the other face side of the semiconductor wafer 7. The semiconductor wafer 7 is heated from one face side with the radiation heat from the hear source 1, the infrared rays radiated from that zone 7c of the semiconductor wafer 7 which is not in contact with the susceptor 4 are measured by an infrared radiation thermometer 6, and the measurement values are fed back to the heat source.
However, the actual production of such apparatuses proved difficult it to make the feed-back control. That is, a part of the infrared rays from the infrared lamp 1 entered the infrared radiation thermometer 6 through the susceptor 4 to make the thermometer give a wrong indication temperature. The temperature of the semiconductor wafer needs to be controlled within an extremely high precision of, for example, .+-.0.5.degree. C. Therefore, suppressing the infrared transmittance of the susceptor 4 to around 1% is certainly sufficient in improving the heat response of the susceptor, but causes a large error in the indication temperature of the infrared radiation thermometer with the result that the temperature varies at the wafer and the treated state of the wafer varies within the wafer surface.